Valentineâs Day began in a happy frame of mind for many of the 3,200 students arriving at Marjory Stoneman Douglas high school, some clutching handmade love hearts for classmates and flowers for their teachers.

But by the end of the day, 17 people would be dead, allegedly killed by a former student, 19-year-old Nikolas Cruz, who had been expelled from the school for unspecified disciplinary reasons. The mass shooting is at least the eighth episode involving gun death or injury at a US school this year.

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Terrified teenagers huddled together with their teachers in classrooms, closets and bathrooms as the gunman, armed with smoke grenades, a semi-automatic AR-15 assault rifle, and wearing a gas mask, moved from room to room, opening fire indiscriminately.

Aaron Feis, a football coach and security guar d, is said to have stepped directly into the path of the bullets to protect his students. According to reports in the Miami Herald, he fell to the ground as a female student he was shielding screamed into her cellphone on a call with her mother. It was not immediately clear if the coach had survived the shooting. Late on Wednesday, several victims were still undergoing surgery and fighting for their lives in Broward county hospitals.

â[The shooter] went and set off the fire alarm so the kids would come pouring out of the classrooms into the hall,â Bill Nelson, a US senator, told reporters. âAnd there the carnage began.â

It was, in the words of Scott Israel, the sheriff of Broward county, simply âanother horrific day, a detestable day â¦ Iâm absolutely sick to my stomach to see children who go to school with backpacks and pencils lose their livesâ.

The massacre began at about 2.30pm, close to dismissal time, when the killer entered the campus and set off the alarm.

It was the second fire alarm of the day, students said. The first had been a planned drill but the second siren alerted some that something was not right.

Staff shouted at their students to get into classrooms quickly as the shooter began his killing spree. Some teachers immediately slammed their classroom doors shut and instructed students to hide by the walls.

Children used their cellphones to text parents and livestream images, some of the videos featuring c haos and screaming. One girl told a local television news crew that she saw a teacher shot dead in front of her as he tried to lock the classroom door. It remained open as the killer passed on by in the hallway.

One 15-year-old student, seeing the gunman enter his classroom, decided to lie on the floor pretending to be dead, according to 23-year-old Sivan Odiz, a local resident and family friend who spoke to the boy after the massacre.

âBut when he got up, there were two people killed,â Odiz told the Guardian as she waited outside the school for news on other friends she had not heard from.

Sarah Crescitelli, 15, cowered in the schoolâs drama building as she heard more shots ring out. She tried to reassure her classmates that all would be OK and sent her mother a text message: âIf I donât make it I love you and I appreciated everything you did for me.â

A police SWAT team eventually arrived, instructing Crescitelli and other students to raise their hands and run for the exit. âIâm shocked,â she said. âI didnât really think it could happen, but Iâm just glad that Iâm OK.â

Play Video 2:26 17 confirmed dead in 'horrific' attack on Florida high school â" video report

Another girl, who sought refuge under desks in a classroom with fellow students, told how the shooter tried to get them to come out. âHe was taunting us, going âhey, heyâ, screaming at us like he wanted to get us out. But we wouldnât,â she said.

After the rampage was over, the gunman was seen leaving the high school and heading towards Westglades middle school, which shares a campus with Stone man Douglas.

From there he disappeared, but police quickly apprehended Cruz at a house in Coral Springs, about a mile away, after he was identified by a teacher.

âThere was no confrontation. He was taken into arrest without incident,â Israel said, adding that Cruz had âcountlessâ magazines of ammunition with him.

Investigators who looked at Cruzâs social media pages on Wednesday found things that were âvery, very disturbingâ, Israel said without elaboration. By nightfall, Cruz was under interrogation by FBI agents and detectives at Broward police headquarters.

Cruz, who had worked at a Dollar Tree store close to the high school after his expulsion, was described by students as a disturbed young man who often spoke about violence and guns.

Mutchler said he had fallen out of touch with Cruz after his expulsion â" but Cruz had bragged to him in the past about firing his air rifle in his backyard during target practice.

âHe just changed,â agreed Victoria Olvera, 17, who struggled to hold back tears as she spoke. âAs far as I knew, he was like a future school shooter.â Olvera clutched a photograph of a close classmate who had not yet been accounted for, worried she may have been killed.

âItâs not real,â she said in disbelief. âItâs not real at all.â

By 9pm, at an evening press conference, Israel said 12 of the 17 victims had been identified, although their names would not be released until their families had been informed. Some were adults, some were children, he said. âWe lost a football coach from Stoneman Douglas High tonight.â

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For Israel, who a little more than a year ago was handling a mass shooting at Fort Lauderdale international airport, the tragedy struck close to home. His own three children, triplets, once attended and graduated from Stoneman Douglas.

Doctors at Broward Health said 17 patients were taken to three hospitals in the area. One was the shooter, who was treated briefly for an unidentified injury, and released to police custody.

Medical staff would not discuss patientsâ ages, injuries or conditions, but said that of the eight patients at Broward North medical centre, two had died, three were in a critical condition and three stable.

âWe have penetrative trauma, non-penetrative trauma, thatâs what we do every day,â said emergency medicine director Igor Nic hiporenko. Of the three still in surgery on Wednesday night, he said: âTheyâre going to have successful surgeries, theyâre going to recover, theyâre going to go home.â

Facebook Twitter Pinterest Students reunited with parents after the shooting. Photograph: Giorgio Viera/EPA

Throughout the evening students, many visibly traumatised, had been taken from the school to a local Marriott hotel where many were questioned by law enforcement before being released back to their families who had assembled en masse outside.

John Crescitelli, a family doctor and 15 year-old Sarah Crescitelliâs father, was shaking as he was reunited with his daugh ter. He feared she had been killed.

âThese school shootings have to stop. This is crazy. My sonâs football coach died. Itâs horrible,â he said. âItâs like Columbine across the street from my house.â

Asked by the Guardian if the tragedy should lead to stricter gun control for people with mental health issues, he replied: âI donât want to get into a gun debate. I really donât. What are you going to do? Confiscate everybodyâs guns? We have millions and millions of weapons â¦ Iâm a gun owner. I donât want the government taking my gun.â

âAll the regulation in the world wouldnât have prevented necessarily what happened today. Itâs something thatâs tragic, but what regulation can you pass that takes away the guns that are already out there?â he said.

His son was waiting to hear if one of his close classmates was among the de ad. By late Wednesday evening, Irwin said, the student was still missing.

Such a perspective was not shared by Israel, who argued during an evening press conference that people with mental health issues should not be able to purchase or use firearms.

Among those absent from the debate was Donald Trump. By the late evening, reports emerged that the president would not be speaking in public about the mass shooting, despite aides advising him otherwise.

Earlier in the day Trump had tweeted a message to send his âprayers and condolencesâ, adding: âNo child, teacher or anyone else should ever feel unsafe in an American school.â